Measurement Automation Strategy: Key to Bio-Ethanol ... - Krohne

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Measurement Automation Strategy: 

Key to Bio-Ethanol Refinery Efficiency 

By Hemant Narayan, Industry Specialist 

February 2008 Copyright KROHNE, Inc.

Measurement Automation 

Strategy Key to Bio-Ethanol 

Refinery Efficiency 

KROHNE White Paper Measurement Automation Strategy Key to Bio-Ethanol Refinery Efficiency 

By Hemant Narayan 

Introduction 

The conversion of corn into fuel 

ethanol is once again gaining 

popularity and is an appealing 

business opportunity for farm 

communities and agribusinesses 

in the mid-west and other 

regions of the U.S. and Canada. 

Investors are attracted by the 

prospect of more than doubling 

the monetary value of a bushel of 

corn by converting it into 2.75 

gallons of fuel ethanol, 17 

pounds of animal feed, and other 

value added byproducts. 

In the U.S. alone, over 120 plants 

are now producing ethanol from 

corn feedstock, and another 76 

are under construction. Dozens 

more are in various stages of 

planning, with total domestic 

production capacity expected to 

double during the next five years. 

The Des Moines Register 

recently reported that farmers 

planted more corn in 2007 than 

in any year since 1944, based on 

expectations of increased 

ethanol production. 

The rapid increase in production 

reflects the expanding market 

for bio-ethanol, driven by 

growing recognition of the 

economic, social and 

environmental benefits of 

biofuels. Ethanol is increasingly 

in demand as an octane-enhancing 

substitute for the additive MBTE, which 

is being banned in many states. The 

2005 Energy Policy Act stimulated the 

growth of this industry by offering 

federal incentives and goals for 

replacing a portion of our nation’s 

gasoline requirements with a 

renewable fuel source by 2012. Current 

estimates indicate we will surpass 

these benchmarks well before 2012. 

Fourteen billion gallons of ethanol 

would be required, if an E10 (10%) 

blend were to replace all 140 billion 

gallons of gasoline consumed in the 

U.S. annually. Add to this a strong push 

from state legislatures for the market 

adoption of E85 (85%) blends, and the 

growing interest in Canadian and 

overseas markets, and it is easy to 

understand the high level of investment 

in new production capacity. 

Thin Profit Margins 

The strong demand, however, 

represents only one part of the 

profitability equation. The whole 

proposition is not profitable if 

inefficiencies in the production process 

itself add significant costs, as a result 

of excess energy consumption, poor 

yields, wasteful use of raw materials, 

process chemicals and enzymes. 

Unfortunately, in many cases, that is 

exactly what’s happening. 

The cost of natural gas and other 

utilities are especially problematic, as 

these items far exceed the other major 

cost components, including the cost of 

plant construction and labor. For 

example, in a typical plant, the natural 

gas that fuels boilers, evaporators, 

February 20, 2008 2 of 12



dryers and other equipment 

comprises 15% of the cost of 

producing a gallon of ethanol. 

For a 100MGY plant, that 

translates to millions of dollars 

in operating costs. Conserving 

energy by just 1% improves the 

bottom line by tens of thousands 

of dollars. 

The elevated price of natural gas 

is not the only financial 

challenge. When an ethanol 

production facility comes online, 

the increased local demand for 

corn puts upward price pressure 

on corn prices and poses 

problems with variability of 

feedstock. Some ethanol 

producers report that ethanol 

yields vary as much as 7 percent, 

depending on the variety of corn. 

Lower yields add considerable 

financial risk – an anathema to 

investors. 

Need for Tight Process Control 

For these reasons, achieving 

consistent profitability can be a 

tough challenge for bio-ethanol 

producers. An individual ethanol 

producer has little influence on 

the market price it receives for 

the product it ships and little 

control over the price of 

feedstock and natural gas. What 

ethanol producers can do – must 

do – is tightly control their own 

manufacturing process, and 

thereby produce consistently 

high yield, while minimizing the 

consumption of energy and raw 

materials, such as yeast, 

enzymes, nutrients, and chemicals. 

As any business guru will tell you, 

process control depends on accurate 

and reliable measurement. Process 

improvement methodologies, such as 

Lean Manufacturing and Six Sigma, are 

fundamentally measurement-based 

strategies that seek to maximize 

productivity while eliminating variation. 

In fact, measurement is both the second 

step and the fifth step of the Six Sigma 

DMADV process (define, measure, 

analyze, design, verify). However 

implementing process control 

strategies requires a careful 

understanding of process needs, 

including identifying measurement 

challenges and applying an optimal, 

customized solution that takes 

advantage of the best available 

technology. 

Importance of Meter Selection and 

Placement 

Careful selection and installation of 

measurement devices is important for 

three reasons: 

Measurement Accuracy. 

First and foremost, measurement 

devices give visibility to the process, 

allowing plant operators to “see” what 

is going on inside the pipes and 

production systems and how full each 

tank is. This is actionable information 

that provides the basis for planning and 

management systems and for real-time 

process control. To be useful, this 

information must be accurate. 


Automation. 



Accurate and reliable 

measurement devices enable 

automation by programmable 

logic controllers and computer 

systems. Automation improves 

plant efficiency and production 

consistency. Measurement 

devices should have selfdiagnostics 

and alarming 

capabilities to automatically 

monitor conditions on a continual 

basis and to alert operators of 

problem states such as changes 

in flow caused by solids, 

entrained gas, or temperature 

changes, as well as problems 

with the functioning of the 

measurement device itself. 

Maintenance Costs. 

High performance measurement 

devices may have a higher initial 

purchase cost, but they will 

typically have lower total lifetime 

costs, because of the elimination 

of downtime for recalibration 

and repair. Some manufacturers 

now offer interchangeable 

components, such as a universal 

signal converter that is 

compatible with a variety of 

meters with different sensor 

technologies or different pipe 

diameters and flow rates. This 

flexibility greatly simplifies 

engineering, procurement, and 

parts inventory. 

Measurement Devices 

Measurement devices serve several 

purposes in an ethanol plant. 

Flowmeters 

Flowmeters measure the speed and 

volume (or, in some cases, the mass) of 

liquids and gases that move through a 

pipe, including beer, stillage, syrup, 

enzymes, water, steam, CO2 and 

natural gas, as well as methane used as 

an alternate fuel. A wide variety of 

flowmetering technology is available, 

including Coriolis, magnetic, ultrasonic, 

variable area, and vortex-based 

devices. 

Density meters 

Density meters measure the percent 

solids during feed stock preparation. 

Density meters also measure the final 

alcohol quality (proof) to monitor and 

control energy intensive processes and 

to satisfy ASTM documentation 

requirements for selling final products 

into the transport fuel distribution 

system. 

Level meter 

Level meters indicate the volume of 

solids or fluids in a tank, for process 

control and inventory management. 

Mechanical devices that utilize 

hydrostatic pressure are fast being 

replaced by more accurate and reliable 

direct level measuring technologies 

such as guided wave radars and noncontact 

methods that employ radar and 

ultrasonic waves. 

Other Measurements 

At various points in the production 

process, it is also necessary to measure 




and control temperature -- 

during cooking, fermentation and 

distillation, for example – as well 

as other attributes such as 

pressure, pH, conductivity, and 

moisture. 

Achieving High Performance 

Every stage of production 

demands precision, and a plant’s 

measuring device supplier must 

have a deep understanding of the 

entire ethanol production 

process, as well as the best 

technology available and suitable 

for each type of measurement 

required. 

Performance is not just a 

question of selecting the best 

technology and device for the 

particular application. Proper 

placement of the device in the 

pipeline or tank is also critically 

important to ensure not only 

accurate measurement but also 

to avoid distortions, clogging and 

damage. Achieving good 

performance and controlling 

total lifecycle costs also depends 

on a preventive maintenance and 

periodic calibration checks on 

some instruments. 

The Production Process 

This white paper provides 

examples of how accurate 

measurement improves 

efficiencies and contributes to 

profitability in a typical dry 

milling process during the five 

main parts of the production 

process: conversion, 

fermentation, distillation, dehydration, 

and recovery of byproducts (e.g., CO2, 

and DDGS). 

Conversion 

Conversion, the first step of the dry 

milling process, converts the starch in 

the feedstock to simple sugars in 

preparation for the subsequent 

fermentation process. Such conversion 

is not necessary for sugarcane and 

other sugar-rich feedstock sources, 

because they do not contain starches 

that need to be converted into 

fermentable sugars. 

Corn feedstock is processed using 

enzymatic conversion. The feedstock is 

ground into fine particles and mixed 

with water to prepare corn mash, a 

consistent slurry. The grinding process 

increases surface area and frees the 

starches from inside the protective cell 

walls. Alpha amylase enzymes are 

typically used for the liquefaction of the 

starch-rich grain. A second enzyme, 

glucoamylase, is commonly used to 

convert the liquefied starch into 

glucose (simple sugar) in a process 

called saccharification. 

Cellulosic feedstock requires more 

complex hydrolysis conversion to break 

down the closely-bonded cellulose and 

hemicellulose from the lignin and 

release the fermentable sugars. 

Once the feed stock has been converted 

to fermentable sugar, the downstream 

steps of the dry milling process – 

fermentation, distillation and 

dehydration – do not tend to vary by 

type of feedstock. 


Fermentation 



Fermentation employs yeast to 

convert the glucose into ethanol. 

Fermentation can be done in 

batches or continuously when 

combined with saccharification. 

Depending on yeast strain, 

fermentation can take one to five 

days. Yeast dosage is dependant 

on the sugar content and the 

desired percent of alcohol at the 

end of the fermentation process. 

Fermentation severely slows 

after reaching 14% alcohol, 

because alcohol denatures the 

process. However, some types of 

yeast can ferment up to 21%. 

Tightly controlling temperature 

is critical to maximizing 

efficiency, because fermentation 

will usually cease above 85°F. 

The fermentation process 

produces “beer” containing 

diluted alcohol and solids. Two 

downstream processes, 

distillation and dehydration, 

extract the liquid and purify it in 

steps to achieve 100% alcohol 

content (200 proof) as required 

for E100 fuel ethanol 

specification. 

Carbon dioxide (CO2) 

Carbon dioxide (CO2), a second 

co-product of the ethanol 

production process, is given off 

in large quantities during 

fermentation. As a gas, CO2 is 

colorless, odorless, and 

incombustible. In its liquid form, 

CO2 reaches an extreme -17°F, 

which makes it an excellent 

source for cooling and freezing 

applications. CO2 vapors released from 

fermentation are usually scrubbed to 

recover any alcohol vapors and cleaned. 

If sold to commercial users, the CO2 is 

liquefied. Otherwise, it is typically 

released back into atmosphere. 

Distillation 

Distillation is the process by which 

alcohol is separated from the mash and 

water. It exploits the difference in 

boiling points between alcohol and 

water. Distillation can only purify the 

ethanol to about 94% alcohol (6% 

water), because water and alcohol form 

an azeotrope at atmospheric pressure. 

Dehydration 

Dehydration A molecular sieve is the 

simplest method and most common 

method of purifying ethanol from 190 to 

200 proof. 

Evaporation and Drying 

Evaporation and Drying The solids 

waste at the bottom of (a?) beer well is 

processed separately in a 

centrifuge/evaporation/drying process 

to produce distillers dried grains with 

solubles (DDGS). Distillers grains are 

rich in cereal proteins, fat, minerals, 

and vitamins, and they serve as an 

excellent source of digestible protein 

and energy. 

Each area of the plant described briefly 

above – milling, slurry preparation, 

liquefaction, fermentation, distillation, 

dehydration, evaporation and drying — 

requires a measurement solution that 

provides an optimal relationship 

between performance and purchase 




price. This performance includes 

not only accuracy, but also 

reliability and durability, as well 

as frequency and method of 

calibration, and lifetime 

maintenance costs. 

Optimizing Solids Measurement 

Most production operators 

understand the importance of 

percent solids control for an 

effective fermentation process, 

and measurements are routinely 

conducted at various points in 

the process. Unfortunately, most 

percent solids measurements 

are performed only periodically, 

by a laboratory moisture 

analyzer. Although the lab 

analyzer may be calibrated for 

high accuracies, this sampling 

and testing process usually 

proves unreliable in practice, 

and is extremely difficult to get 

repeatable results. 

As a result, an increasing 

number of plant operators are 

opting for real-time, online 

measurement to continuously 

monitor the contents of the 

mixing tank and make 

instantaneous changes to the 

process. Plants are thereby able 

to maintain process 

requirements within acceptable 

tolerances (typically within 

0.5%). This real time 

measurement and control allows 

more consistency in the slurry 

mix solids and enables operators 

to push the solids percentage 

higher, thereby reducing flow 

problems and enzyme usage and other 

costs. Continuous monitoring of solids 

concentration facilitates the detection 

and prompt correction of any slow 

decrease in solids. 

By continually measuring percent 

solids, a record is established for each 

fermentation batch. The data facilitates 

realistic prediction of the outcome of 

the fermentation process, in order to 

optimize the overall process by 

reducing problems with previous known 

flow issues. The solids data can also 

be used to improve the beer well 

averages, a key factor in increasing 

alcohol yields. 

The newest generation of industrial 

grade Coriolis meters has proven to 

provide highly accurate and repeatable 

density measurements, as the basis of 

good solids measurement. 

Unfortunately, the “bent” design and 

internal flow splitters in previous 

generations of Coriolis meters 

frequently failed due to fouling and 

blockages. These problems have been 

eliminated by the single, straight tube 

OPTIMASS 7000 series coriolis meters 

developed by KROHNE, Inc. The single, 

straight tube design provides an 

affordable, accurate and highly reliable 

solids measurement solution. 

Optimizing Ethanol Rectification and 

Dehydration 

Rectification and dehydration provide a 

textbook case of the importance of 

accurate measurement for effective 

process control. 

The rectification and dehydration are 

common to any fuel ethanol process, 

whether wet milling, dry grind or 




cellulosic. The goal of the 

rectification process is to achieve 

maximum purification (up to 190 

proof). Then the dehydration 

process employs molecular 

sieves to convert the 190 proof 

ethanol into 200 proof ethanol, 

going from 5% moisture content 

to 0%. 

If the process fluid moves too 

quickly through the molecular 

sieves and some moisture 

remains, then the entire batch 

must be run back through the 

dehydration system again – a 

completely inefficient step that 

wastes energy and ties up 

production capacity and 

potentially causes a bottleneck 

for the entire plant. To avoid this 

problem, a plant could extend 

the dwell time in the molecular 

sieves to ensure that all 

moisture is removed. However, 

this margin of comfort comes at 

a cost in terms of productivity 

loss and unnecessary energy 

consumption. 

Alcohol proof measurement of 

rectifier output (190 proof) and 

dehydration output (200 proof) 

can dramatically improve 

process efficiency. Precise 

density measurements, detects 

exactly when the ethanol reaches 

the anhydrous threshold (zero 

moisture content), so that the 

dehydration process can meet its 

target without overreaching, 

thereby obviating the need for 

any wasteful comfort margin. 

As with the percent-solids 

measurement application discussed 

above, the new generation of Coriolis 

meters with single, straight tube 

design, has proven to be a highly 

accurate and reliable solution for realtime 

monitoring of alcohol proof during 

the rectification and dehydration 

processes. The continuous trends data 

allows for instantaneous correction of 

process upsets and ensures the 

consistent and tight control of proof 

values in final product. This process 

control is critical to meeting quality 

control specifications and to increasing 

throughput and profitability. 

An important advantage of the state-ofthe-art 

Coriolis meters, such as the 

KROHNE 7000 Series T80 OPTIMASS 

meter, is the ability to measure 

multiple parameters in a single device – 

proof, density, temperature and flow. 

Previously, plant operators needed to 

purchase, install, calibrate and 

maintain several separate devices to 

perform all these functions: typically 

one meter would measure density and 

proof on a slipstream, and additional 

instruments would be installed in the 

main line to measure temperature and 

flow. 

More Efficient Dryer Operation 

Single straight tube Coriolis meters, 

with multiple-parameter capability, 

also provide high pay backs when 

installed on the evaporator syrup draw. 

Installations of an online flow/density 

meter at the intermediate and final 

stages of the evaporator process have 

successfully demonstrated significant 

reductions in energy consumption, by 




tightly controlling the syrup 

percent and flow rate through 

the evaporators. 

Running syrups at higher solids 

is desirable, because less 

moisture means less work for 

the dryers and therefore lower 

energy consumption in the drying 

process. Higher solids 

percentage (i.e., lower moisture 

content) can be achieved by 

reducing the flow rate through 

evaporators which increases 

retention time. Unfortunately, 

lower flow rates can cause 

extensive build up inside the 

lines and can also affect the 

evaporator efficiency, and line 

plugging can cause costly 

downtime. For these reasons, 

plant operators need to manage 

the process to maintain the 

optimal solids level at all times. 

As with other processes, the 

continual, automated 

measurement by coriolis meters 

facilitates better control than 

offline lab samples. The single, 

straight tube design of the 

KROHNE Coriolis meters 

mitigates the maintenance and 

reliability problems that can 

plague conventional "bent tube" 

Coriolis meters, especially given 

the high solids content and 

viscosity of the syrup. The 

KROHNE Coriolis meters employ 

adaptive sensing technologies 

(AST), a patented design makes 

accurate measurements even of 

mixtures with high viscosity or 

solid matter content and the 

straight-tube design causes less 

pressure drops than other flowmeters, 

resulting in lower energy costs. 

Volumetric Flow metering 

Upstream of fermentation, dry-milling 

ethanol plants make extensive use of 

inline electromagnetic flowmeters to 

measure flows containing high solids 

content, such as backset, corn slurry, 

mash, beer, as well as on whole, thick 

and thin stillage. Most magnetic 

flowmeters available in the market 

today use a pulsed DC technology which 

has replaced older AC technology that 

had inherent problems with drift and 

zero stability. However, pulsed DC 

magnetic flowmeters have performance 

limitations, especially with noisy 

applications such as slurry. 

These problems can be addressed by 

using the KROHNE IFC3000 signal 

converters with digital noise filtering 

and a low-noise electrode 

configuration. For demanding, highsolids 

applications, KROHNE’s 

advanced magnetic flowmeters provide 

self-diagnostic capabilities for 

detecting sensor coating degradation 

and predicting electrode or liner 

failure, in order to minimize failures 

and expensive downtimes. 

The multiple-parameter capability of 

some magnetic flowmeters, such as the 

KROHNE OPTIFLUX 4300C, provides an 

added benefit during CIP procedures. 

The CIP wash includes flushing the 

lines and recirculation chemical in a 

specific sequence, such as acid-wateralkali-water. 

By using the conductivity 

measurement feature built into the 

flowmeter, the process can be 




controlled automatically and 

remotely to ensure a more 

efficient CIP cycle, facilitating 

chemical reuse and reducing 

waste. 

Applications downstream of the 

rectification process pose a 

challenge for magnetic 

flowmeters due to very low 

conductivities. In such cases, 

alternative technologies, 

including vortex shedding and 

ultrasonic, provide a better 

solution. Flowmeters with 

moving parts, such as turbines 

and paddle wheel, are prone to 

coating and mechanical failure. 

The KROHNE UFM3030 inline 

triple beam ultrasonic flow 

meters have demonstrated 

better value over competing 

vortex shedding technologies 

due to high accuracy and 

repeatability over a wider 

turndown. 

Controlling Steam Consumption 

Flowmeters also play a critical 

role in controlling energy 

consumption by measuring the 

flow of steam used extensively in 

cooking, dehydration and 

evaporation. Steam 

measurements are performed on 

a mass flow basis, even though 

the high moisture contents in 

saturated steam vapors causes 

failure of true mass flow sensing 

designs such as Coriolis and 

thermal mass meters. 

Consequently, volumetric 

devices such as orifice plates or 

vortex meters are extensively 

used. Unfortunately, most of these 

volumetric devices measure the velocity 

of steam in the pipeline and compute 

volumetric flow rate from the line size. 

When outputting mass flow, they use a 

fixed density correction to convert 

volumetric flow to mass flow, usually 

calculated around a fixed operating 

pressure. This fixed correction will 

cause significant errors in the final 

mass flow during inevitable changes of 

the operating pressure (density) of the 

steam. Field tests show that a 10% 

change in saturated steam line 

pressure can cause a fixed-density 

compensated meter to over/under read 

by up to 25%, even though the primary 

volumetric measurement from meter is 

well below 1%. 

The KROHNE OPTISWIRL 4070 

multivariable steam meter was 

designed specifically to overcome these 

challenges. It precisely measures flow 

rate, pressure and temperature with 

integrated sensors and provides 

accurate density compensation for 

highly accurate mass flow 

measurement independent of operating 

conditions. The fully-welded stainless 

steel construction makes the 

measuring tube of the OPTISWIRL 

highly resistant to pressure, 

temperature, corrosion and aging and 

provides high immunity to water 

hammer even of wet steam 

applications. 

Accurate steam metering is critical not 

only for controlling the flow of steam 

and regulating temperature, but it also 

provides a dependable means for 

determining loss and wastage. 

February 20, 2008 10 of 12

Improved Inventory Management 



Level meters play an important 

role in improving the plant’s 

bottom line by enabling tighter 

inventory management and 

process control. For example, 

accurate measurement allows 

close tracking of the use of the 

enzymes in the slurry tanks 

during the mash preparation 

process, and of the chemical 

consumption in the clean-inplace 

routines. Measurement of 

the level in fermentation tanks 

enables the regulation of foam, 

which can be a challenge when 

controlling a fermentation 

process. Level measurement is 

also critical to operating 

reboilers and distillation tanks, 

as well as final storage tanks. 

Simply put, you need to know 

exactly how much material you 

have, and how much you are 

using. 

Reboilers, Distillation Tanks 

and Final Storage 

For reboilers, distillation tanks 

and final storage 

tank farms, the KROHNE BM26A 

side mount level 

gauge offers high reliability over 

technologies that have problems 

measuring under tough 

conditions of vacuum, high 

temperatures, vapor phases and 

foaming. 

Some level measuring systems 

deployed use hydrostatic 

pressure to measure from the 

bottom of the tank. This is an 

indirect method of measurement that 

assumes a constant density to 

determine the actual surface level. 

However, when the temperature 

changes, the density of the medium will 

change, causing a change in pressure, 

even though the level of material in the 

tank has not changed. Pressurized 

tanks need additional compensation. 

An alternative approach is to use noncontact 

radar or guided radar level 

devices to directly detect the level from 

the top of the tank. These methods 

measure distance and they are 

unaffected by pressure changes, vapors 

or tank pressure. Top-of-tank 

placement also makes repair or 

replacement easier. Bottom-of-tank 

implementations can only be serviced 

when the tank is empty — a rare 

occurrence in active, high-volume 

plants. 

Return on Investment 

Ethanol production holds great promise 

for our country’s energy future and also 

provides an excellent opportunity to 

support our domestic agricultural 

economy and communities. 

Investments in plant infrastructure 

today will yield benefits for years to 

come. 

As more and more plants come online, 

competition naturally increases among 

producers. As the market matures, it 

will demand the highest possible 

quality at the lowest price. In this 

economical environment, producers 

will maintain profitability only by 

controlling production costs, reducing 

waste, and conserving energy wherever 

possible. 

February 20, 2008 11 of 12



Investing in the plant’s 

measurement systems both 

during new construction or 

retrofit, is one area that has been 

proven to offer high returns in 

the form of increased 

productivity and lower costs. 

February 20, 2008 12 of 12

Measurement Automation Strategy: Key to Bio-Ethanol ... - Krohne

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